add nn_ref_apr option in namsbc_apr

namsbc_apr

@@ -2,7 +2,7 @@
 &namsbc_apr    !   Atmospheric pressure used as ocean forcing           (ln_apr_dyn =T)
 !-----------------------------------------------------------------------
    rn_pref     = 101000.   !  reference atmospheric pressure   [N/m2]/
-   ln_ref_apr  = .false.   !  ref. pressure: global mean Patm (T) or a constant (F)
+   nn_ref_apr  =   0       !  ref. pressure: 0: constant, 1: global mean or 2: read in a file
    ln_apr_obc  = .false.   !  inverse barometer added to OBC ssh data
 
    cn_dir = './'        !  root directory for the Patm data location
@@ -10,4 +10,5 @@
    !           !  file name              ! frequency (hours) ! variable  ! time interp.!  clim  ! 'yearly'/ ! weights filename ! rotation ! land/sea mask !
    !           !                         !  (if <0  months)  !   name    !   (logical) !  (T/F) ! 'monthly' !                  ! pairing  !    filename   !
    sn_apr      = 'patm'                  ,         -1.       ,'somslpre' ,   .true.    , .true. , 'yearly'  ,    ''            ,    ''    ,      ''
+   sn_apref    = 'mean_patm'             ,         -1.       ,'meanapr'  ,   .true.    , .true. , 'yearly'  ,    ''            ,    ''    ,      ''
 /